1. Field of the Invention
The present invention generally relates to a radiation shield in a light detector and/or sensor assembly.
More particularly, the invention relates to the use of a shielding arrangement comprising the combination of a radiation shield, a buffer, and a collimating buffer.
2. Description of the Prior Art
Some types of light detectors or sensors must be cooled in order to be useful. Other types of detectors or sensors are often cooled to improve their ability to detect (their sensitivity) or to improve their stability by reducing the noise level and/or maintaining a stable environment. As is known, cooling is more important in the infrared region of light wave detection or measurement.
In the prior art, single- or multiple-stage thermoelectric cooling devices or liquid nitrogen have often been used to cool detectors or sensors.
In light detectors or sensors, a critical consideration is the noise level encountered in the course of detection or measurement. The source of the noise is dependent upon the type of detector or sensor in use, as well as the design of the detection or measurement instrument and/or the nature of the object being monitored or measured.
A problem which arises in the prior art technology relates to the fact that, by cooling alone, one may still not be able to reduce the noise level of the detector or sensor to a desirable level. Such a problem is encountered when the noise source is light radiation characterized by a wavelength within the detector's sensitive wavelength region. Such light radiation may be generated from other parts of the instrument, or may comprise scattered radiation from an optical system.
Accordingly, it is considered desirable, in light of the prior art, to design a cooling mechanism which not only provides for cooling of the detector, but also provides shielding against any stray radiation. Ideally, the temperature of such a shield should be kept near the detector's temperature.
When a thermoelectric cooling device is used as a cooling media, the high temperature junction of the cooler is often in the same detector or sensor package. Moreover, the temperature of the enclosing case is often as high as that of the high temperature junction of the cooler.
Furthermore, radiated light from the hot junction or base plate is often scattered by the assembly enclosure, by the window of the detector assembly, or by the components outside of the assembly package, and this radiation is detected by the sensor or detector. This contributes to the noise level experienced with respect to the detector or sensor.
In addition, if one increases the current applied to a thermoelectric cooling device (for example, in order to improve the ability of the detector to detect), more heat will be generated at the hot junction of the cooling device. Unless the heat dissipating capability of the base plate of the assembly is improved as the current is increased, the case temperature will rise by a considerable amount, and the noise level may be increased.
The resulting radiation not only reduces the ability of the detector or sensor to detect, but also can induce erroneous results. For example, in a two-color pyrometer, one must measure the intensity ratio of radiation emitted from a target in two wavelength regions. If the optical system is such that only one wavelength region of light from the hot junction of the thermoelectric cooler is reflected into the sensor by the filter of the instrument, the measured result is incorrect.
Accordingly, it is considered desirable to develop a radiation shield for use within a sensor or detector assembly, wherein radiation from the hot junction of the cooler, radiation from the enclosure, and/or radiation from other than the target, which enters into the sensor or detector assembly, can be minimized. Furthermore, it is considered desirable to develop a radiation shield for use in a sensor or detector assembly, wherein electromagnetic noise associated with the thermoelectric cooler does not adversely affect the very low-level high-impedance signal generated by the detector when a relatively unstable and high current is applied to the cooler.